Floor scrubbing machines are widely used to clean the floors of industrial and commercial buildings. They range in size from a small model which may clean a path ranging from perhaps 15 inches up to 36 inches wide controlled by an operator walking behind it, tio a large model cleaning a path as wide as five feet controlled by an operator riding on the machine. Such machines in general are wheeled vehicles with suitable operator controls. Their bodies contain power and drive means, a solution tank to hold clean scrubbing solution and a recovery tank to hold soiled solution recovered from the floor being scrubbed. A scrub head which contains One or more scrubbing brushes and means to drive them are attached to the vehicle by a jointed linkage system, and may be located in front of, under or behind it. A water distribution system dispenses scrubbing solution from the clean water tank to the floor in the vicinity of the scrubbing brush or brushes and there is a system to recover soiled scrubbing solution from the floor after it has been scrubbed. Solution recovery is the primary area with which this patent is concerned. Other areas of concern will also be described later.
In general, the solution recovery system comprises a double lipped vacuumized squeegee that wipes the floor behind the scrub head and collects the soiled scrubbing solution, which is comprised of water, detergent and soilage that has been loosened from the floor. A flexible hose and rigid ducting as needed connect the squeegee to the upper part of the recovery tank in the body of the vehicle where the soiled solution is stored. A high volume vacuum fan pulls air from the top of the recovery tank and exhausts it to atmosphere, which creates a sub-atmospheric pressure in the tank that draws air through the ductwork from the squeegee. The air velocity is high enough at the squeegee that the soiled scrubbing solution is entrained in the air stream and carried to the recovery tank. There the air spreads out, thus losing velocity, so that the solution drops into the tank while the air is exhausted to atmosphere by the fan.
It is important that only clean air passes through the fan. Soilage, water and detergent mixed with the air cause blade abrasion and bearing damage in the fan and cause it to blow out unacceptable pollution into the surrounding atmosphere. Therefore the soiled scrubbing solution must be completely separated from the air stream before the air reaches the fan.
Achieving this has been a long-standing challenge in scrubber design. The high air velocity needed for good water pickup in a vacuum squeegee together with turbulence of the conveying air stream in the ducts may break down some of the conveyed solution into a mist which can remain airborne and be drawn into the fan. Also, many detergents used in floor cleaning generate foam when they are agitated, and can produce enough foam on the surface of the water in the recovery tank to reach the fan inlet and blow through it before the recovery tank is full. Foam can also come from the soilage that is scrubbed from industrial or commercial plant floors, which will sometimes contain high foaming agents. A recovery tank is normally sized to recover the contents of the solution tank after application to the floor and also provide an air plenum space, but excessive foam can necessitate shutting down the machine and emptying the recovery tank before the solution tank is empty, which reduces the productivity of the machine.
Prior art has addressed the problem. U.S. Pat. No. 4,393,538 describes a four way approach comprising a gradually enlarging duct from the squeegee hose to the recovery tank to slow the air stream velocity with a minimum of agitation, a direction reversing baffle in the recovery tank, a filter ahead of the fan inlet, and a clean water mist sprayed on the foam to break it down. The air plenum space above the liquid in the recovery tank is recommended to be of sufficient volume that the air in it will change not more than 60 times per minute, with fewer changes preferred.
Such measures have proven to be quite effective in the larger sizes of scrubbers such as shown in the illustrations of the '538 patent. Large scrubbers provide sufficient height to accommodate an expanding air duct of effective length going up from their squeegee hoses to their recovery tanks, and their recovery tanks are large enough to provide adequate space between the air entry from the squeegee duct and the air exit into the fan inlet.
Small scrubbers, such as the common walk-behind models, lack these advantages. Scrubber squeegees commonly must swing from side to side to track the water path from the brushes in turns, so a flexible suction hose is needed going up from the squeegee. The height of a large machine accommodates a flexible hose of adequate length and above it a rigid duct which may have an expanding cross section. A small walk behind machine typically turns sharper than a large machine, so its squeegee must swing farther and will need a longer flexible hose. But the small machine has much less height. Typically the required length of flexible hose reaches nearly to the top of the machine and connects directly to the upper part of the recovery tank. This leaves no space for an expanding duct between the squeegee hose and the recovery tank as described in the '538 patent. Yet a small machine requires as much air velocity for water pickup as a large machine and has the same need for slowing down that air velocity to avoid foaming.
Also, as one might expect, the recovery tank used on a small machine is reduced in size to match the scale of the machine. On prior art small scrubbers the fan is typically set directly above the recovery tank, which together with the smaller tank has made a far shorter distance inside the tank from the squeegee hose outlet to the fan inlet than the large machines have. Thus they have had less settling of foam and mist before the air reached the fan.
From the above it can be seen that other means than those described in the prior art are needed to settle water out of the air stream and control foam in small walk-behind scrubbers.